[ELM] Functions generated from operationId can have invalid names

Description

The operationId field of paths can have values which are not valid Elm identifiers. It seems that these values are used unmodified to produce Elm function names, meaning that the generator produces invalid Elm code.

This happens, for example, when operationId values contain "."s, as is common when using connexion.

Swagger-codegen version

2.4.17

Swagger declaration file content or url

basePath: /
consumes:
- application/json
info:
  description: An API
  title: An API
  version: '1.0'
paths:
  /:
    get:
      operationId: get.foo.bar
      responses:
        '200':
          description: Success
produces:
- application/json
swagger: '2.0'

Command line used for generation

swagger-codegen generate -i broken.yaml -l elm -o gen

Steps to reproduce

1. Put the above YAML into broken.yaml
2. Run the command above

Suggest a fix/enhancement

At least for my purposes, replacing '.' with '_' in the function names would do the trick. There may be more characters in valid operationId's which are invalid in Elm identifiers, though, so someone who knows the spec should find all translations that need to happen.

Start by running the provided broken.yaml declaration with swagger-codegen generate -i broken.yaml -l elm -o gen, then inspect the generated Elm function name for get.foo.bar. Trace how operationId values reach the Elm output and account for invalid identifier characters; done means the generated code is valid Elm for this example and other invalid operationId values are handled consistently.